Calix[4]pyrrole as a promoter of the CuCl-catalyzed reaction of styrene and chloramine-T

Calix[4]pyrrole, an easy-to-prepare anion receptor, acts to promote the cuprous chloride-catalyzed aziridination of styrene by the nitrene source chloramine-T in acetonitrile. The mechanism of action is believed to involve incipient anion-receptor interactions involving the calix[4]pyrrole NH protons and the chlorine atom of the CuCl, rather than direct bonding to, and activation of, the chloramine-T Consistent with this supposition were the findings that (1) the use of calix[4]pyrrole, in combination with CuCl, did promote enhanced reactivity when PhI=NTs was used as the nitrene source and (2) the presence of calix[4]pyrrole had no effect on the reaction when Cul was used as a catalyst. Decreased yields were also seen with CuCl2, and no appreciable aziridination product was observed when the calix[4]pyrrole was replaced by an appropriately chosen dipyrromethane control compound. On the other hand, the enhancement effect provided by calix[4]pyrrole proved relatively insensitive to the presence of trace quantities of water.